The accurate measurement and monitoring of physiological parameters, including blood volume pulse (BVP), heart rate (HR), respiratory wave (RW), and respiration rate (RR), plays an important role in a wide variety of applications in healthcare, psycho-physiological (polygraph) examinations, and sports training. In particular, dynamic changes in physiological parameters can reveal changes in the physiological status and function of a patient.
Traditional techniques for the measurement of physiological parameters require sensors to be attached to a subject. The attachment of sensors to a subject can cause undesirable skin irritation and discomfort. In particular, it may be undesirable to affix sensors to patients during sleep studies (when they may influence a subject's sleep patterns) or during sports training (when they may adversely influence an athlete's mobility). In some cases, contact-based measurements have also been shown to influence the underlying physiological parameter(s) being measured. As a result, there is a great interest in methods of measuring and monitoring physiological signals by non-contact means. While many methods of remotely measuring physiological parameters have been investigated, the ability to distinguish the physiological parameter(s) to be measured in a subject from background, such as environmental noises and movement artifacts, is deficient or limited.
Laser Doppler, microwave Doppler radar, and thermal imaging have been investigated for the remote measurement of physiological parameters with varying success; however, all of these systems require expensive and specialized hardware. The ability to measure physiological parameters, including HR and RR, using a conventional video camera has attracted recent interest. See, for example, Takano, C. and Ohta, Y. “Heart rate measurement based on a time-lapse image,” Medical Engineering & Physics, 29:853-857(2007). Though attractive in principle, many of these methods accomplish noise reduction using linear filters, which are ineffective in the event that background noise falls within the same frequency band as the physiological signal of interest. Others have proposed using blind source separation for noise removal. See, for example, U.S. Patent Application Publication No. US 2011/0251493 to Poh, et al. However, blind source separation methods require a multi-channel signal input, restricting their applicability to processing signals collected using a camera which provides a multi-channel signal (such as a color camera that generates a Red, Green, and Blue multiple-channel signal). As a result, these methods cannot be used to determine physiological parameters in conditions when ambient light is insufficient to permit the use of a color camera, such as in a darkened room. Moreover, blind source separation does not provide a method of distinguishing false positives from actual results. Blind source separation will return false physiological parameters when an inanimate object, such as a drawing or picture of a human face, is imaged. This severely limits the applicability of blind source separation methods in many healthcare applications, as it cannot reliably indicate a loss of vital signs in a subject.
Therefore, it is an object of the invention to provide improved methods and systems for non-contact measuring one or more physiological parameters, including blood volume pulse, heart rate, respiratory wave, and respiration rate, in a subject, particularly in low-light conditions.
It is also an object of the invention to provide methods and systems for non-contact monitoring dynamic changes one or more physiological parameters, such as blood volume pulse, heart rate, respiratory wave, and respiration rate, in a subject, particularly in low-light conditions.
It is a further object of the invention to provide methods and systems for distinguishing false positives from actual results when non-contact measuring and monitoring one or more physiological parameters, such as blood volume pulse, heart rate, respiratory wave, and respiration rate, in a subject, particularly in low-light conditions.